portable collapsible negative pressure ic unit for ... portable collapsible negative pressure ic...
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As published in IHE - October 2006
TRIED & TESTED
Kaplan Medical Centre (KMC) and Beth-El Zikhron Yaaqov Industries Ltd (Beth- El) have developed the IsoArk, a collapsible negative pressure isolation chamber that is specifically designed for intensive care situations, and carried out pre- liminary clinical testing of the chamber. The safety and feasibility of treating contagious patients in real-life conditions was investigated.
L. Poles 1 S. Kunicheski 2 Y. Polishuk 2
Introduction Emerging infectious diseases, “classical” highly infectious agents like aspergillosis and tuberculosis are health threats both for the general public and the healthcare providers. Airborne Infection Isolation Rooms (AIIRs) are part of the arsenal of con- tainment and infection control measures for airborne transmissible agents.
In many major cities, hospitals are often at maximum capacity. The extent of the need for AIIRs during a natural outbreak of airborne-transmissible disease, such as severe acute respiratory syndrome (SARS), is anticipated to be very high. For example, dur- ing a few months of the 2003 global SARS epidemic, the National University Hospi- tal in Singapore had to isolate roughly 600 patients in negative pressure conditions . Temporary negative pressure isolation rooms were used as emergency room triage units . Shortage of AIIRs was even worse in Toronto, Canada, where the city’s healthcare infrastructure was overwhelmed with 251 cases, 43 deaths and 27 000 exposed persons, including healthcare workers .
Any healthcare system has only limited number of AIIRs and lacks the patients’ iso- lation capacity to handle a significant event . Fixed AIIRs are not only costly to build, but they require appropriate maintenance procedures. Intensive care treat- ment is associated with aerosol-generating procedures, thus increasing the risk of contagion for the staff of the intensive care unit (ICU), for other patients and the hos- pital in general. Furthermore, the existing fixed AIIRs are not always suited for inten- sive care treatment of isolated patients. There is thus a need for a cost-effective, highly flexible operational concept of a portable AIIR with intensive care capabilities that can be rapidly erected in many areas in any hospital, and in extreme situations even in makeshift healthcare facilities.
Methods The development and testing process of the portable isolation chamber comprised the three following stages: 1. Constructing an IsoArk prototype within the general ICU of KMC, modifying it according to ICU environmental and operational standards and needs. 2. Following intensive briefing and training for the ICU personnel, the efficacy and safety of the chamber were tested by measuring environmental parameters, first without, and later with, continuous actual care of three patients for 48 hours each. The physicians and nurses worked in personal protective equipment (PPE) used for airborne precaution and provided ICU procedures’ care, including standard minimal- ly invasive procedures. 3. Testing the feasibility of erecting the chamber in a non-ICU environment.
Heat- and noise-generating equipment inside the chamber included a Bennet MA2 respirator, monitors, infusion pumps and a computerised patient information man- agement system.
The participating patients were all nongravid adults in stable condition, who did not suffer from contagious disease and gave informed consent to be treated within the chamber. The protocol was approved by KMC’s ethics committee.
General description of the isolation chamber As a result of suggestions made by the end-users in stages 1 and 2 of the testing process, the construction underwent some modifications as follows: the system con- sists of a main chamber and an integrated airlock (Figure 1). The overall size of the main chamber in the prototype tested was 3.05 m x 3.81 m x 2.30 m. The skeleton is based on a light metal frame. No floor covering is used, but a double seal attached to the bottom portion of the liner provides a seal with the floor through the negative pressure inside the chamber and the weight of the framework. The walls and ceiling are made of non-permeable, detergent- and disinfectant-resistant, fire-retardant sin- gle-layer PVC. The plastic is transparent, allowing observation into the contained environment from the outside and minimising confinement sensation. Curtains hung on the outside provide privacy when needed.
Tool conduits in the sidewalls of the main chamber provide access for probes, hoses and cables for supply and data support systems, minimising the need for equip- ment decontamination and disposal. Cables that are leading to panels with elec- tricity and medical gas ports hang on an inner skeleton, providing support to equip- ment within the chamber. An interchangeable window offers access to a chest X-ray machine or provides glove-box access for routine checks and management of the patient. The chamber is separated from the outside by an airlock with wide double swingdoors. The filtration unit automatically switches to a high flush mode for an adjustable amount of time when someone enters the airlock, maximising protection while minimising delay when leaving the chamber. One of the walls has an opening into a patent container for contaminated laundry, used PPE and other contaminated material.
A single, independent filtration unit creates three stages of airflow: 1. “Night” mode with an airflow rate of 1000 m3/hr, 2. “Day” mode with an airflow rate of 1400 m3/hr, and 3. “Airlock flushing” mode with 2200 m3/hr (automatically initiated upon entrance to the airlock) providing up to 1000 air exchanges per hour depending on the airflow.
A pre-filter and a high efficiency particulate air (HEPA) filter provide a minimum fil- tration efficiency of 99.995% , as required by the EN-1822 standard. An ultraviolet (UV) radiation unit is incorporated in the filtration unit. The latter contains audiovi- sual alarm systems and visual information concerning the pressure gradient between the chamber and the external world.
Objective safety parameters collected throughout the experiment inside and outside the isolation chamber included air temperature, humidity, noise, CO2 and O2 con- centration levels, as well as pressure gradients. Pre-defined safety levels were CO2 > 3% and O2
Safety parameters (Table 1) Maximal in-chamber CO2 levels measured were 320 ppm (empty chamber) and 339 ppm (chamber occupied by a patient and a member of staff ). Minimal O2 levels were 20.6% and 20.2% respectively. Maximal noise levels were 65dB when empty and 62dB when operational. (Note: the overall environmental noises of the total ICU were also picked up and calculated in this figure. Refer to Table 1 for the noise level of the unit). The maximal noise level delta was 7 dB, i.e. noisier outside the chamber than inside! The maximal temperature inside the chamber when opera- tional was 24°C and maximal delta temperature in those conditions was 1°C. Maximal in-chamber humidity measured when operational was 55%, while maximal humidity gradi- ent was 3% in these conditions.
Efficacy parameters (Table 1) As stated previously, the efficacy of the filtration unit was pre-evaluated by the manu- facturer. Operational efficacy was defined as the ability to maintain adequate pressure gradient when the isolation chamber was operational, expressed as the minimal pres- sure gradient throughout the stay of the patient with at least one of the doors closed. That minimal gradient was -6 Pascal between the main chamber and the interlock, -3 Pascal between the interlock and the outside environment and -10 Pascal between the main chamber and outside.
Subjective assessment On a scale of 1 to 10, the ICU staff graded their subjective preliminary experience with the portable AIIR as follows (average values): * ease of breathing in the main chamber =6.2 * freedom of claustrophobic sensation = 6.8 * noise level = 3.3 * ease of external communication = 3.5 * ease of internal communication = 7.8 * general access to patient = 6.5 * ease of providing medication = 8.1 * ease of invasive procedures = 7 * washing the patient = 7.8 * making the patient’s bed = 8 * suctioning the patient = 6.8 * visual contact with the monitor = 6.3 * control of the respirator = 8.3 * control of the infusion pumps = 7.9 * ease of moving inbound through the airlock = 8.2 * moving outbound = 8.6 * using PPE within the airlock = 7 * passing through the airlock:
laboratory samples = 7.7 laundry = 7.6 a visitor = 7.1
* using waste disposable unit = 7.6
Additionally, many nurses pointed out that the increased level of stress and opera- tional constraints while working inside an isolation room call for reinforcement of the nursing staff.
Basic operational feasibility in a non-ICU setting The AIIR was erected in the physical therapy gymnasium. This place is already equipped to serve as an alternative ICU in case a surge capacity is needed. In less than 45 minutes the isolation chamber was operational.
Discussion The AIIR was incorporated in the ICU environment without posing safety problems to patients or healthcare providers as observed or measured during field testing. As learned during the SARS epidemic, it is recommended that nursing manpower be strengthened to accommodate the greater stress and efforts resulting from working in full PPE inside the AIIR. Further technical improvement considered are a two-way communication system, the inclusion of a hand-disinfecting unit inside the airlock, and adding external patient monitors. Other portable units were developed, but none were oriented for intensive care treatment and no field testing has been done.
As early as 19